Certain improvements have been made in the present invention so that the bicycle chain transmission can be efficiently operated on all kinds of road surface with minimum effort labor.
In a regular bicycle chain transmission, a crank is generally fastened in the center of a chain wheel. During pedaling, the moment arm of the crank does not make any change. It is known that a longer moment arm of a crank can minimize effort in forward pedaling. Therefore, there is a prior art structure employing a chain wheel of oval shape so that the moment arm of the crank can be automatically changed during its rotation. This type of design can effectively minimize effort in pedaling. However, a chain may be easily disengaged from an oval shaped chain wheel during rotation.